Process for converting ethylene to light alpha olefins

ABSTRACT

A process for producing light alpha olefins by ethylene oligomerisation in contact with a catalyst produced by mixing a zirconium compound with an organic compound selected from the group formed by acetals and ketals, with an aluminum hydrocarbyl compound selected from the group formed by chlorine-containing or bromine-containing aluminum hydrocarbyl compounds and with an aluminum hydrocarbyl compound selected from tris-(hydrocarbyl)-aluminum compounds.

This is a divisional of application Ser. No. 09/030,161 filed Feb. 25,1998. Now U.S. Pat No. 6,103,654

The present invention relates to a process for producing light alphaolefins by oligomerisation of ethylene in contact with a Ziegler-typecatalyst produced by mixing a zirconium compound with an organiccompound selected from the group formed by acetals and ketals, with analuminium hydrocarbyl compound selected from the group formed bychlorine-containing or bromine-containing aluminium hydrocarbylcompounds and with an aluminium hydrocarbyl compound selected fromtris-(hydrocarbyl)-aluminium compounds.

A number of zirconium compounds have been used to oligomerise ethyleneto alpha olefins, generally associated with various other ligands.

Examples are the use of zirconium halides associated with esters,ketones, ethers, amines, nitrites, anhydrides, acid chlorides, amides oraldehydes, described in U.S. Pat. No. 4,855,525 and International patentapplication WO 91 02707, or the use of the same zirconium halidesassociated with ligands selected from the group formed bysulphur-containing, phosphorous-containing or nitrogen-containingcompounds, described in European patents EP-A-0 241 596 and EP-A-0 328728.

The products obtained with the catalytic formulae given above areprincipally constituted by alpha olefins with a chain length of betweenC₁₀ and C₁₈.

U.S. Pat. No. 5,345,023 describes a process for producing light alphaolefins, principally 1-butene, 1-hexene, 1-octene and 1-decene, byoligomerising ethylene, using a catalytic composition obtained by mixinga zirconium compound with an organic compound selected from the groupformed by acetals and ketals and with a chlorine-containing orbromine-containing aluminium hydrocarbyl compound. The teaching of thispatent is included in the present application.

We have now discovered that the addition of atris-(hydrocarbyl)-aluminium to the above catalytic composition cangreatly increase the activity.

More precisely, the improved catalytic composition is obtained bymixing:

at least one zirconium compound with formula ZrX_(x)Y_(y)O_(z), where Xis a chlorine or bromine atom, Y is a radical selected from the groupformed by alkoxy RO⁻, amido R₂N⁻, or carboxylate RCOO⁻ groups, where Ris a hydrocarbyl radical containing 1 to 30 carbon atoms, x and y havewhole number values of 0 to 4 and z is equal to 0 or 0.5, the sum x+y+2zbeing equal to 4;

with at least one organic compound with formula (R₁′)(R₂′)C(OR₁)(OR₂)where R₁′ and R₂′ are constituted by a hydrogen atom or a hydrocarbylradical containing 1 to 30 carbon atoms, R₁ and R₂ being hydrocarbylradicals containing 1 to 30 carbon atoms;

with at least one aluminium compound with formula AlR″_(n)X_(3−n) whereR″ is a hydrocarbyl radical containing 1 to 6 carbon atoms, X is achlorine or bromine atom, and n is a number in the range 1 to 2;

and with at least one aluminium compound with formula AlR′″₃ where R′″is a hydrocarbyl radical containing 1 to 6 carbon atoms.

Preferably, the composition also comprises at least one solvent,advantageously selected from the group formed by aliphatic,cycloaliphatic and aromatic hydrocarbons, and compounds corresponding toby-products of oligomerisation such as high oligomers. The solvent ispreferably selected from aromatic hydrocarbons; ortho-xylene isparticularly suitable.

Reference should be made to U.S. Pat. No. 5,345,023 for the preparationof the catalytic composition.

Examples of zirconium compounds are zirconium halides such as zirconiumtetrachloride ZrCl₄, zirconium tetrabromide ZrBr₄, alcoholates such aszirconium tetrapropylate Zr(OC₃H₇)₄, zirconium tetrabutylate Zr(OC₄H₉)₄,carboxylates such as zirconium 2-tetraethyl hexanoate Zr(OCOC₇H₁₅)₄ oroxocarboxylates such as dizirconium 2-oxohexaethyl hexanoate[Zr(OCOC₇H₁₅)₃]₂O.

The organic compounds selected from the group formed by acetals andketals used in the invention result from condensing an aldehyde orketone with a mono-alcohol or a poly-alcohol, for example a glycol. Theyhave the following general formula:

 (R₁′)(R₂′)C(OR₁)(OR₂)

where R₁′ and R₂′ are constituted by a hydrogen atom or a hydrocarbylradical containing 1 to 30 carbon atoms and R₁ and R₂ are hydrocarbylgroups containing 1 to 30 carbon atoms. The two radicals R₁′ and R₂′ andthe two radicals R₁ and R₂ may be identical or different. They can alsoform a ring. Examples are diethoxymethane, diisopropoxymethane,1,1-diethoxyethane, 1,1-diisobutoxyethane, 1,1-dimethoxydecane, 2-nonyl-1,3-dioxolane, 2,2-dimethoxyoctane, 1,1-dimethoxycyclohexane, andpreferably 2,2-dimethoxypropane, 2,2-dibutoxypropane,2,2-dihexyloxypropane, 2,2-dioctoxypropane, and2,2-di-(2-ethylhexyloxy)-propane.

Examples of the aluminium compounds used in the invention represented bygeneral formula AlR″_(n)X_(−n)-are chlorodiethylaluminium,dichloroethylaluminium, and preferably ethylaluminium sesquichloride, ormixtures thereof.

Examples of the aluminium compounds used in the invention represented bygeneral formula AlR′″₃ are trimethylaluminium, tributylaluminium,trihexylaluminium, and preferably triethylaluminium.

Particularly advantageously, the catalyst so resulting from theinteraction of a mixture of at least one zirconium compound, such aszirconium tetrachloride, and at least one organic compound selected fromthe group formed by acetals and ketals, resulting from condensing analdehyde or a ketone with a mono-alcohol or a poly-alcohol, such as2,2-di-(2-ethylhexyloxy)-propane, with at least one chlorine-containingor bromine-containing aluminium hydrocarbyl compound, such asethylaluminium sesquichloride, and with at least onetris-(hydrocarbyl)-aluminium, such as triethylaluminium.

The catalyst components can be brought into contact in any order in asolvent selected from the group formed by aliphatic hydrocarbons andcycloaliphatic hydrocarbons such as hexane, cyclohexane or heptane,aromatic hydrocarbons such as toluene or xylenes, and by-products ofoligomerisation such as high oligomers. Advantageously, aromatichydrocarbons are used, preferably ortho-xylene. The zirconium compoundis preferably first mixed with the acetal or ketal then the aluminiumcompounds are added to the mixture, in any order or themselves as amixture.

The molar ratio between the acetal or ketal and the zirconium compoundis 0.1:1 to 5:1, preferably 0.5:1 to 2:1. The molar ratio between thechlorine-containing or bromine-containing aluminium hydrocarbyl and thezirconium compound is 1:1 to 100:1, preferably 5:1 to 50:1. The molarratio between the tris-(hydrocarbyl)-aluminium and the zirconiumcompound is 0.01:1 to 10:1, preferably 0.1:1 to 2:1. The concentrationof zirconium in the catalytic solution so prepared is advantageously inthe range 10⁻⁴ to 1 mole per liter, preferably 10⁻³ to 0.5 moles perliter. The temperature at which the four components are mixed isnormally in the range −10° C. to 180° C., preferably in the range 0° C.to +150° C., for example a temperature close to ambient temperature (15°C. to 30° C.). The mixture can be formed in an atmosphere of ethylene oran inert gas.

The solution or catalytic composition produced as above can be used asit is to carry out the oligomerisation reaction, or it can be diluted byadding a solvent selected from the group formed by aliphatic,cycloaliphatic and aromatic hydrocarbons, and by-products ofoligomerisation such as high oligomers. Aromatic hydrocarbons arepreferably used, preferably ortho-xylene.

The process is carried out under oligomerisation conditions, atpressures of 0,5 to 15 MPa, and at temperatures of 20-180°0 C.

In a process for carrying out batchwise catalytic oligomerisation, therequired volume of the catalytic solution prepared as described above isintroduced into a reactor provided with the usual stirring and coolingsystems, then pressurised with ethylene to a pressure which is generallyin the range 0.5 to 15 MPa, preferably in the range 1 to 10 MPa, and thetemperature is generally maintained between 20° C. and 180° C.,preferably between 40° C. and 150° C. The oligomerisation reactor issupplied with ethylene at a constant pressure until the total volume ofliquid produced represents between 2 and 50 times the volume of thecatalytic solution originally introduced. The catalyst is thendestroyed, for example by injecting an amine into the reactor, then thereaction products and any solvent are extracted and separated from anysolvent.

The operation of a continuous process is preferably as follows: thecatalytic solution is injected into the reactor at the same time as theethylene, the reactor being stirred by conventional mechanical means orby external re-circulation. The catalyst components can also be injectedseparately into the reaction medium, for example the product of theinteraction of the zirconium compound with the acetal or ketal, and themixture of the two aluminium compounds. The temperature is kept between20° C. and 180° C., preferably between 40° C. and 150° C., and thepressure is generally adjusted to between 0.5 and 15 MPa, preferablybetween 1 and 10 MPa. The liquid level in the reactor is kept constant.Ethylene is introduced via an inlet valve, which is pressure controlled,which keeps it constant. The reaction mixture is extracted from thereaction zone using a valve controlled by the liquid level. This mixtureis sent to a catalyst destruction zone which comprises injection of anamine, for example, then vaporisation of the effluent treated with theamine, either by raising the temperature, or by reducing the pressure,or by simultaneous action on the temperature and the pressure, torecover the products in the vaporised fraction. The products and anysolvent are then separated in a system of distillation columns. Theunreacted ethylene can be returned to the reactor. The catalyst residuesincluded in a heavy fraction can be incinerated.

The following examples illustrate the invention without limiting itsscope.

EXAMPLE 1

2×10⁻³ moles of sublimed zirconium tetrachloride was transferred into a100 ml glass flask in an inert atmosphere in the absence of moisture,then 45 ml of dry, de-aerated ortho-xylene was injected using ahypodermic syringe. 2×10⁻³ moles of 2,2-di-(2-ethylhexyloxy)-propane insolution in 5 ml of ortho-xylene was added to the white suspension,which was stirred at ambient temperature using a magnetic stirrer. Overa period of several minutes, the zirconium chloride dissolved and ahomogeneous yellow solution formed.

5 ml of the solution of the zirconium complex formed above, i.e.,0.2×10⁻³ moles of zirconium, 50 ml of ortho-xylene, then a mixture of0.2×10⁻³ moles of triethylaluminium and 1.2×10⁻³ moles of ethylaluminiumsesquichloride Al₂Et₃Cl3 in solution in 10 ml of ortho-xylene wereintroduced in that order into a stainless steel autoclave with a workingvolume of 250 ml provided with a double envelope to regulate thetemperature by circulating oil or water, in an argon atmosphere atambient temperature. The temperature was then raised to 90° C. whileintroducing ethylene into the autoclave so as to keep the pressure at aconstant 6 MPa.

After 2 hours of reaction, ethylene introduction was stopped. 5×10⁻³moles of 2-ethylhexylamine in solution in 3 ml of ortho-xylene was theninjected into the autoclave under pressure using a trap which could bepressurised to a pressure above that of the autoclave. The autoclave wasthen depressurised and a gaseous fraction and liquid fraction wererecovered which were analysed by chromatography.

The material balance of the reaction showed it to be formed of 92.3 g ofoligomers, corresponding to a specific activity of 10140 g ofoligomers/g of zirconium/hour. The oligomer composition was as follows:

butenes 25.2% by weight 1-butene 98.8% hexenes 22.6 1-hexene 96.5octenes 16.9 1-octene 94.0 decenes 12.9 1-decene 86.6 heavy compounds22.4

EXAMPLE 2 Comparative

This example used the same procedure as that described for Example 1 toprepare the zirconium complex solution. The catalyst was used in thesame autoclave, but the triethylaluminium was omitted and the onlyaluminium compound used was thus ethylaluminium sesquichloride in thesame quantity and at the same concentration as that of Example 1.

The ethylene oligomerisation reaction was carried out under the sameconditions as in Example 1 and over the same reaction period. At the endof the reaction, 2-ethylhexylamine was injected into the autoclave inthe same quantities and using the same technique as described forExample 1.

The material balance of the reaction showed it to be formed of 59 g ofoligomers, corresponding to a specific activity of 6486 g of oligomers/gof zirconium/hour. The oligomer composition was as follows:

butenes 25.5% by weight 1-butene 96.2 hexenes 24.1 1-hexene 95.8 octenes17.7 1-octene 93.9 decenes 13 1-decene 85.6 heavy compounds 19.7

Comparison of this example of the prior art with Example 1, which was inaccordance with the invention, shows the clear superiority of theinvention.

EXAMPLE 3

The reaction was carried out in a pilot unit operating in continuousmode. It comprised a perfectly stirred reactor with a total volume of 3liters, operating with a liquid level control of 2 liters. In thisreactor, where the temperature was regulated to 135° C. by oilcirculation and the pressure was maintained at 8.5 MPa using a valvelocated on the ethylene inlet line, 17.2 g/h of a solution of 1 kg ofortho-xylene containing 0.37 g of sublimed zirconium chloride and 0.45 gof 2,2-di-(2-ethylhexyloxy)-propane, and 17.2 g/h of a solution of 1 kgof ortho-xylene containing 5.9 g of aluminium sesquichloride and 0.19 gof triethylaluminium, also 493 g/h of ortho-xylene, were continuouslyinjected.

Under these conditions, the ethylene flow rate at the reactor inlet,which was pressure controlled, settled at 259 g/h. The oligomerproduction was 136 g/h, corresponding to a productivity of 54.5 kg/g Zr.The oligomer composition was as follows:

butenes 28.6 % by weight 1-butene 99.7% hexenes 25.0 1-hexene 98.loctenes 18.3 1-octene 96.4 decenes 12.2 1-decene 93.0 heavy compounds15.9

EXAMPLE 4 Comparative

The reaction was carried out in the same apparatus using the sameprocedure as described in the previous example. In this reactor, wherethe temperature was regulated to 135° C. by oil circulation and thepressure was maintained at 8.5 MPa using a valve located on the ethyleneinlet line, 26 g/h of a solution of 1 kg of ortho-xylene containing 0.38g of sublimed zirconium chloride and 0.46 g of2,2-di-(2-ethylhexyloxy)-propane, and 26 g/h of a solution of 1 kg ofortho-xylene containing 5.9 g of aluminium sesquichloride, also 508 g/hof ortho-xylene, were continuously injected.

Under these conditions, the ethylene flow rate at the reactor inlet,which was pressure controlled, settled at 273 g/h. The oligomerproduction was 130 g/h, corresponding to a productivity of 34.1 kg/g Zr.The oligomer composition was as follows:

butenes 28.8 % by weight 1-butene 99.5 hexenes 26.4 1-hexene 97.7octenes 18.6 1-octene 95.8 decenes 11.6 1-decene 90.6 heavy compounds14.6

Comparison of this example with Example 3 clearly demonstrates theadvantage of the catalyst of the invention.

What is claimed is:
 1. A process for converting ethylene to light alphaolefins comprising oligonerizing ethylene under oligomerizationconditions in contact with a catalytic composition obtained by mixing:at least one zirconium compound with formula ZrX_(x)Y_(y)O_(z), where Xis a chlorine or bromine atom, Y is a radical selected from the groupconsisting of alkoxy RO, amido R₂N, and carboxylate RCOO groups, where Ris a hydrocarbyl radical containing 1 to 30 carbon atoms, x and y havewhole number values of 0 to 4 and z is equal to 0 or 0.5, the sum x+y+2zbeing equal to 4; with at least one organic compound with formula(R₁′)(R₂′)C(OR₁)(OR₂) where R_(1′ and R) ₂′ being a hydrogen atom orhydrocarbyl radicals containing 1 to 30 carbon atoms, and R₁ and R₂being hydrocarbyl radicals containing 1 to 30 carbon atoms; with atleast one aluminum compound with formula AlR″_(n)X_(3−n) where R″ is ahydrocarbyl radical containing 1 to 6 carbon atoms, X is a chlorine orbromine atom, and n is a number in the range 1 to 2; and with at leastone, tris-(hydrocarbyl) aluminum compound with formula AlR′″₃ where R′″is a hydrocarbyl radical containing 1 to 6 carbon atoms.
 2. A processaccording to claim 1, characterized in that the catalytic compositionalso contains at least one solvent selected from the group consisting ofaliphatic, cycloaliphatic and aromatic hydrocarbons, and high oligomerby products of oligomerisation.
 3. A process according to claim 2,characterized in that the solvent is an aromatic hydrocarbon.
 4. Aprocess according to claim 3, characterized in that the solvent isortho-xylene.
 5. A process according to claim 1, characterized in thatthe zirconium compound and the organic compound are mixed, the productobtained then being mixed with the aluminium compounds.
 6. A processaccording to of claim 1, characterized in that the organic compound isdiethoxymethane, diisopropoxymethane, 1,1-diethoxyethane,1,1-diisobutoxyethane, 1,1-dimethoxydecane, 2-nonyl- 1,3-dioxolane,2,2-dimethoxyoctane, 1,1-dimethoxycyclohexane, 2,2-dimethoxypropane,2,2-dibutoxypropane, 2,2-dihexyloxypropane, 2,2-dioctoxypropane, or2,2-di-(2-ethylhexyloxy)-propane.
 7. A process according to claim 1,characterized in that the zirconium compound is zirconium tetrachloride.8. A process according to claim 1 characterized in that the twoaluminium compounds are ethylaluminium sesquichloride andtriethylaluminium.
 9. A process according to claim 1, characterized inthat the molar ratio between the organic compound and the zirconiumcompound is in the range 0.1:1 to 5:1.
 10. A processed according toclaim 1, characterized in that the molar ratio between thechlorine-containing or bromine-containing aluminium hydrocarbyl and thezirconium compound is in the range 1:1 to 100:1.
 11. A process accordingto claim 1, characterized in that the molar ratio between thetris-(hydrocarbyl)-aluminium compound and the zirconium compound is inthe range 0.01:1 to 10:1.
 12. A process according to claim 1,characterized in that the catalyst components are mixed at a temperaturewhich is in the range −10° C. to 180° C.
 13. A process according toclaim 2, characterized in that the solvent is used during mixing of thecompounds.
 14. A process according to claim 7, characterized in that thetwo aluminum compounds are ethylaluminum sesquichloride andtriethylaluminum.
 15. A process according to claim 14, characterized inthat the molar ratio between the chlorine-containing orbromine-containing aluminum hydrocarbyl and the zirconium compound is inthe range 1:1 to 100:1.
 16. A process according to claim 15,characterized in that the molar ratio between thetris-(hydrocarbyl)-aluminum compound and the zirconium compound is inthe range 0.01:1 to 10:1.
 17. A process according to claim 16,characterized in that the molar ratio between the organic compound andthe zirconium compound is in the range 0.1:I to 5:1.